Thermohaline Circulation Demonstration

Summary

This activity helps the students to visualize the effects of temperature and salinity on water density, and the resulting thermohaline circulation. Important processes visualized in this demonstration are upwelling, downwelling, and the formation of haloclines, thermoclines and pycnoclines. In addition, mixing by advection is clearly demonstrated.

Context

Audience

undergraduate introductory oceanography course of mostly non-majors

Skills and concepts that students must have mastered

Students should be able to understand the concept of conservative properties, as well as the effects of salinity and temperature on water density.

How the activity is situated in the course

This is a classroom demonstration/exercise usually performed after students have been introduced to the concepts of seawater density and its dependence on salinity and temperature, as well as the controls on temperature and salinity of seawater. Sometimes I will do the demonstration before I introduce the topic of thermohaline circulation in the deep ocean, and sometimes I do it afterwards.

Goals

Content/concepts goals for this activity

salinity and temperature as conservative properties and ability to predict the salinity and temperature of a mixture if the proportions are known

effect of salintiy and temperature on density of water

upwelling and downwelling processes

concepts of thermocline, halocline and pycnocline

Higher order thinking skills goals for this activity

determination of salinity and temperature of a mixture

prediction of behavior of waters of different salinities and temperatures

Teaching Notes and Tips

I find it most useful to have the students make calculations and predictions along the way. One variable that always changes is the last step where the red mixture is added to the tank, because it is very hard to introduce that water without a vertical velocity component. Therefore, it usually goes to the bottom but then is pushed back up above the blue very salty water eventually. A lot of mixing occurs, but this can also be useful for the students to visualize how mixing can occur and the result on the salinity and temperature (the less blue, the less salty; the less intense the yellow, the less warm. I have only two tanks, so I do this as a demonstration with classroom participation. However, it could also be done as a student activity in a lab if there were enough tanks for students to work in small groups.

Assessment

Students hand in their sheets at the end of the class and I go over their answers and predictions to gauge their understanding of the concepts demonstrated. I also ask them one on one whether they are better able to visualize upwelling and downwelling after seeing the demonstration.

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This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

Provenance

Created by the author of the page containing
this file.

Reuse

This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

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Cynthia Venn, Bloomsburg University of Pennsylvania

Reuse

This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.